GENERAL
INTEREST
57
10/2002
Elektor
mally, with nickel as the catalyst. However,
the hydrocarbon fuel makes a nickel-based
SOFC coke up, so this cell has a copper cer-
met anode with a ceria catalyst to directly
oxidise the fuel.
According to Dr. Gorte: “In our earlier
work, we were unable to feed liquid diesel to
the fuel cell because we did not have a
means for vapourising fuels that have a low
vapour pressure at room temperature. This
paper demonstrated that we could feed these
liquids to a fuel cell using a method analo-
gous to a fuel injector in an internal combus-
tion engine and still get stable operation of
the fuel cell.”
The experimental fuel cell operates in a
furnace set at 700 degrees Celsius. A com-
mercial, self-contained fuel cell would ideally
generate that heat itself using the fuel placed
in it. Such a temperature obviously precludes
its use for notebook computers, mobile
phones, etc. (unlike the Motorola and NEC
devices which operate at much lower tem-
peratures); but it still leaves a wide range of
applications, such as automotive and
portable power generators. Although the lab-
oratory device is tiny — approximately 3 mm
square in area, as Dr. Gorte said: “There are
no intrinsic reasons for us to work with such
small cells, but it is easier for us and the
materials questions remain unchanged.”
(020123-1)
ated within the fuel cell from the liq-
uid fuel. Last year, researchers
announced a multi-layer ceramic
technology for processing and deliv-
ering the fuel and air to the MEA.
They have now integrated many of
those other components, including a
methanol concentration sensor and
liquid-gas separation for CO
2
release, directly in the ceramic
device. Miniature pumps and control
and conversion electronics are also
built into the device. The experi-
mental assembly (see
Figure 1
)
measures about 50
×
100
×
10mm
(without electronics or fuel); and
produces over 100 mW net power
continuously.
Work on the RHFC is also dedi-
cated to integrating all the parts.
Previous systems have used discrete
metal components to vapourise the
methanol fuel, reform the methanol
to hydrogen, and clean up the output
of the reformer. Using the multi-layer
ceramic technology, researchers
have demonstrated an integrated
vapouriser and miniature methanol
steam reformer, and a separate
chemical heater — three of the key
components. The reformer assembly,
measuring 38
×
13
×
1mm, integrates
both the fuel vapouriser and
methanol steam reformer. The chem-
ical heater, with the same dimen-
sions, converts a percentage of the
methanol fuel into heat to drive the
reformer reaction. The plan is to pro-
duce an integrated device giving 1
watt or more.
Nanotubes
and nanohorns
The NEC development was achieved
in a joint effort with the Japan Sci-
ence and Technology Corporation
and the Institute of Research and
Innovation. In this, the porous car-
bon electrodes are replaced by ones
made from carbon nanotubes, or,
more accurately, carbon nanohorns
— a variation in shape. Both were
discovered by Sumio Iijima, an NEC
Research Fellow. The main charac-
teristic of the nanohorns is that
when many of them group together
an aggregate of about 100 nm is cre-
ated. This not only gives an
extremely large surface area, but
also makes it easy for the gas and
liquid to permeate through it.
Nanohorns are easily prepared to
high purity, so it is expected to
become a low cost raw material. In
addition, because a nanohorn is pro-
duced by the laser ablation method,
if a platinum catalyst is also simulta-
neously evaporated, a platinum par-
ticle will naturally adhere to the sur-
face of a nanohorn, thus obviating
the conventional and costly wet
process, and compensating for the
costly platinum — at least to some
extent.
Diesel-powered?
Turning now to Pennsylvania Uni-
versity, Dr. Raymond J. Gorte, pro-
fessor of chemical engineering, and
colleague Dr. John M. Vohs, profes-
sor and chair of chemical engineer-
ing, developed a butane powered
fuel cell — the first to run on any-
thing other than hydrogen. Now they
have developed the first to run
directly on a readily available liquid
fuel.
It is a solid oxide fuel cell
(SOFC). This differs from the preced-
ing type in having a solid oxide elec-
trolyte (through which oxygen ions
migrate — giving a greater choice of
fuels), and ceramic electrodes — nor-
Figure 2. Demonstrating that today’s low temperature fuel cells, while not exactly compact,
have the potential to power small electronic devices like a PDA.
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